This invention relates to an apparatus and method for jet noise suppression involving control of the static pressure of the jet and control of the rate of entrainment of ambient fluid into the jet downstream of the exhaust nozzle, and more particularly, includes a long hollow, porous or perforated nozzle plug centerbody through which the static pressure in the jet may be controlled. As used herein, the term "jet" refers to a strong, well-defined stream of fluid issuing from an orifice and producing noise. The prior art includes devices which deflect the flow within the exhaust nozzle and devices which, by injection or suction in the nozzle proper, seek to vary flow mixing between the jet and the surrounding air. However, these devices are designed to mechanically alter flow properties directly at various locations in the nozzle rather than altering the entire flow field of the jet to control momentum flux downstream of the nozzle.
Preliminary studies have indicated that effective jet noise suppression requires altering of the flow over an extended region of the jet to provide positive control over the momentum change between the jet and the induced flow of ambient air. Since the variation of the momentum flux in the jet field is related through the momentum equations to the Reynolds stresses which are the source of sound, control of static pressure in the jet field is directly related to noise suppression.
Prior art jet noise suppressors have enjoyed limited success. Devices which mechanically altered nozzle flow by modifying nozzle configuration have not significantly reduced jet noise and have definite disadvantages of weight and thrust loss. The various suction/injection devices do not affect the entire flow field of the jet and lack adjustment parameters which could allow continuous efficient operation over a range of jet exit velocities and mass flows. Many of these devices also suffer from increased wave drag and needless sacrifice in propulsive efficiency and fuel economy. Public demand for quiet engines in commercial jet aircraft has grown together with an equally pressing demand for fuel economy in the transportation sector. A jet noise suppressor to be acceptable must also be fuel efficient.
Accordingly, it is an object of the present invention to provide an apparatus and method to suppress jet noise by control of the static pressure in the jet to produce a uniform rate of change of momentum in the jet.
Another object of the present invention is to provide an apparatus and method to suppress jet noise by controlling the rate of ambient fluid entrained into the jet to produce a uniform rate of change of momentum in the jet.
Another object of the present invention is to achieve jet noise suppression through a method and an apparatus which are simple, effective, fuel efficient, lightweight, controllable, and adjustable to engine mass flow conditions.
A further object of this invention is to provide an apparatus and method to permit thrust vectoring.
A further object of this invention is to provide an apparatus and method to improve engine performance by repositioning, weakening or eliminating shock waves formed in and downstream of the engine exhaust nozzle.
An additional object of the present invention is to provide an apparatus and method for sound vectoring in a jet.